I'm introducing myself to set theory. My reference doesn't seem to address the fact that 1/1 = 2/2 = 1. If we make a correspondence between natural numbers and rational numbers using sequential fractions, should we just skip equivalent fractions so as to make it a bijection? In other words, does it matter whether the correspondance is injective or not, or whether it is surjective or not? I'm also wondering how one would prove that the set of real numbers in base ten is identical to the set of real numbers in another base.